Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $90.48   13.480%   $102.6767   $102.68   $102.70   $102.70  
  Purchase #2 $89.66   10.794%   $99.3379   $99.34   $99.35   $99.30  
  Purchase #3 $27.45   7.855%   $29.6062   $29.61   $29.60   $29.60  
  Purchase #4 $184.34   7.220%   $197.6493   $197.65   $197.65   $197.60  
  Purchase #5 $196.48   5.494%   $207.2746   $207.27   $207.25   $207.30  
  Purchase #6 $195.47   11.386%   $217.7262   $217.73   $217.75   $217.70  
  Purchase #7 $178.97   6.402%   $190.4277   $190.43   $190.45   $190.40  
  7 purchase totals = $962.85       $1,044.6986   $1,044.71   $1,044.75   $1,044.60